Battery backup or dual battery systems generally include a primary (main) battery and an auxiliary battery. The auxiliary or reserve battery is useful in vehicular battery systems because the auxiliary battery can supply necessary power when the primary battery is drained or malfunctioning. Also, the auxiliary battery can augment the primary battery for high current demand applications or during adverse environmental conditions such as drastically cold weather.
The primary battery and auxiliary battery may be provided in an integrated package as shown in U.S. Pat. No. 5,162,164 or as two separate battery units. The positive terminals of the primary battery and auxiliary battery are coupled together through a manual battery switch. The manual battery switch engages the auxiliary battery when it is in a closed position (conducting state). In vehicular battery systems, the manual battery switch is often located within the integrated battery package, in the engine compartment, under the hood, or proximate some other undesirable place.
Generally, operators of vehicles are not provided any indicia of the state of the manual battery switch or a remote switch to control the battery switch. The state of the battery switch is indicative of whether the auxiliary battery is being engaged. Often, control circuits require a circuit to drive the indicator so that it emits light and a separate circuit to drive the battery switch. Such circuits often require a double pole, single throw (or more complex) switch. However, double pole, single throw switches are more expensive and more difficult to implement because two signal conductors (besides the power and ground conductors) must be coupled to the switch. In vehicular battery systems, each signal wire adds to the manufacturing cost of the vehicle and the potential for defects.
Thus, there is a need for a dual battery system which utilizes an annunciator or indicator as both a circuit element for driving the battery switch and device for providing indicia of the condition of the battery switch. More particularly, there is a need for an indicator and control circuit which utilizes a single pole, single throw switch. The indicator and control circuit should have a low parts count, be highly reliable, and require only a single conductor to connect to the manual switch.